Temperature Rise And Core Loss Varieation Of Soft Magnetic Ferrite During Instant And Continuous Excitation

Soft magnetic ferrite has been widely used as one of most important parts of power electronic converter system. Its volume and power consumption has a decisive influence on the overall efficiency. Therefore, the research and improvement of core loss measurement have a vital significance to the optimal design and reasonable application of magnetic components. This thesis analyzes the composition and source of the core losses firstly, and enumerates several common loss measurement methods. Afterwards, systematic measurement and analysis of the temperature rise in the process of core loss measurement were conducted. Finally, a series of exploratory experiments was accomplished about the variation of temperature and magnetic properties during continuous measurement of core loss.(1) One of the most common phenomena is that the temperature rise of the core will make the properties shift, which should not be ignored in many measurements. We measured the temperature and core loss of PC50 under different magnetizing frequencies and densities and tried to find some relevance between those variables.The results show that: 1.Higher magnetic field intensity and frequency lead to higher temperature rise. 2. The parameters of temperature rise curves under different frequencies and densities of magnetization were fitted by the least squares method and MATLAB based on the core loss formulas. 3. Calculated temperature rise were consistent with experimental data measured previously under the frequencies ranging from 50 k Hz to 1 MHz and magnetic induction intensities ranging from 50 mT to 200 mT.(2)The reliability of electronic products was directly influenced by the stability of soft magnetic ferrite. In order to exploit the reliability of soft magnetic ferrite in the process of continuous excitation from the standpoint of practical use, a series experiments was conducted on the commercial product PC40, PC50, PC90 under different ambient temperature, excitation flux density and frequency. The mean test time was 20-40 min. The test system was based on the B-H analyzer, in addition of the thermocouple to record the temperature variation.Following conclusions were obtained by analyzing the measuring results: 1.Under the same excitation conditions, continuous excitation after 5 min, core loss and temperature tended to be stable at the temperature ranges from 25 to 120 oC. With the increase deviation of temperature away from the bottom temperature of core loss, the difference of stable and initial core loss becomes more and more obviously. 2. As for high-frequency soft magnetic ferrites, the temperature and core loss is apt to be stable under continuous excitation, while the excitation frequency is below 1MHz. As the higher frequency(up to several MHz), core loss will always under the continual change, and especially under high working temperature, it is even more difficult to guarantee the stability. 3. For different sizes of soft magnetic ferrite in homologous series, the initial core losses are almost the same, but higher specific surface area shows smaller core loss variation and temperature rise.4. Temperature rise has a linear relationship with initial core loss. Different series of soft magnetic ferrite show different slop, and the discrepancy of temperature rise tends to be more obviously within higher core loss.In conclusions, the temperature rise formula can be used to estimate the temperature rise and correct possible deviation of measurements results under arbitrary test conditions. The results of temperature and core loss under continuous excitation complement the properties of magnetic material, and favorable to material development and optimal component design.